Alkaline batteries include a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an alkaline electrolyte. The positive electrode active material is commonly manganese dioxide, and there have been various improvements in manganese dioxide in order to improve the discharge characteristics of alkaline batteries.
For example, there has been proposed manganese dioxide in which the amount of structural water (crystalline water) contained in the crystal structure thereof is increased. Japanese Laid-Open Patent Publication No. 2004-186127 proposes the use of manganese dioxide the weight of which changes by 2.7% or more upon heating, in particular, at 200 to 400° C. Also, the 44th Denchi Toronkai Koen Yoshi Shu (the 44th Battery Symposium Abstract Volume) (p. 656-657) states that adjusting synthesis conditions changes the crystal structure of manganese dioxide, thereby resulting in an improvement in the heavy-load discharge characteristics of the battery.
However, in the case of conventional manganese dioxide powder, hydrogen ions cannot move sufficiently in the solid phase of manganese dioxide or in the positive electrode material mixture (i.e., outside the solid phase of manganese dioxide). It is thus difficult to obtain sufficient heavy-load discharge characteristics.
Also, even when the ion movement inside the solid phase of manganese dioxide is sufficiently fast, if the ion movement outside the solid phase is insufficient, it is difficult to sufficiently lessen discharge polarization particularly during heavy-load discharge.